In the manufacture of semiconductor devices and other products, ion implantation systems are used to impart impurities, known as dopant elements, into semiconductor wafers, display panels, or other workpieces. Conventional ion implantation systems or ion implanters treat a workpiece with an ion beam in order to produce n- or p-type doped regions, or to form passivation layers in the workpiece. When used for doping semiconductors, the ion implantation system injects a selected ion species to produce the desired extrinsic material. For example, implanting ions generated from source materials such as antimony, arsenic, or phosphorus results in n-type extrinsic material wafers. Alternatively, implanting ions generated from materials such as boron, gallium, or indium creates p-type extrinsic material portions in a semiconductor wafer.
Conventional ion implantation systems include an ion source that ionizes a desired dopant element which is then accelerated to form an ion beam of prescribed energy. The ion beam is directed at a surface of the workpiece to implant the workpiece with the dopant element. The energetic ions of the ion beam penetrate the surface of the workpiece so that they are embedded into the crystalline lattice of the workpiece material to form a region of desired conductivity. The implantation process is typically performed in a high vacuum process chamber which prevents dispersion of the ion beam by collisions with residual gas molecules and which minimizes the risk of contamination of the workpiece by airborne particulates.
Ion dose and energy are two variables commonly used to define an ion implantation. The ion dose is associated with the concentration of implanted ions for a given semiconductor material. Typically, high current implanters (generally greater than 10 milliamps (mA) ion beam current) are used for high dose implants, while medium current implanters (generally capable up to about 1 mA beam current) are used for lower dose applications. Ion energy is used to control junction depth in semiconductor devices. The energy of the ions which make up the ion beam determine the degree of depth of the implanted ions. High energy processes, such as those used to form retrograde wells in semiconductor devices, typically require implants of up to a few million electron volts (MeV), while shallow junctions may only demand energies below 1 thousand electron volts (keV).
The continuing trend to smaller and smaller semiconductor devices requires implanters with ion sources that serve to deliver high beam currents at low energies. The high beam current provides the necessary dosage levels, while the low energy levels permit shallow implants. Source/drain junctions in complementary metal-oxide-semiconductor (CMOS) devices, for example, require such a high current, low energy application.